Execution Context

Execution Context

JavaScript is loosely typed.
JavaScript is single-threaded and synchronous; it can execute one line at a time in a specific order.

Execution Context Phases

Memory creation phase:
- All variables are defined with undefined as a placeholder.
- In the case of a function, the entire function code is stored.
- An arrow function is also given the value undefined.
Code execution phase:
- Code is executed inside the execution thread.

Hoisting means JavaScript moves declarations to the top of their scope before the code runs.
Formal definition: Hoisting means declarations are processed during the memory creation phase before code executes, which is why variables exist as undefined and functions are fully available before their line is reached.

When a function is invoked, a brand-new execution context is created inside the original execution context.
After the function is executed, or the program is finished, the execution context is deleted.
To simplify the creation and deletion of execution contexts, JavaScript has its own call stack.
When a program is invoked, the entire global execution context is pushed onto the stack. Later, if another execution context is created, it is pushed onto the stack.
Execution contexts are popped out when a function's or the entire program's execution is complete.
The call stack maintains the order of execution of execution contexts.

By default, a window object is created by the JavaScript engine (global is used as the global object in Node.js instead).
this is also created by the JavaScript engine (globalThis === window).
this is the context object.